Apparatus for controlling the feeding of paper in high-speed printers

ABSTRACT

Apparatus for controlling the paper feeding in printing apparatus, wherein the feed motor speed is controlled by the combined effect of a speed-space detector whose output is speedproportional voltage and said pulses are compared with a predetermined pulse number, and wherein the results of said comparison are employed in combination to provide a suitable paper feed power control through a bidirectional amplifier which does not require a stabilized power supply.

United StatesPatent' Bonzano [54] APPARATUS FOR CONTROLLING TIE FEEDINGOF PAPER IN HIGH-SPEED PRINTERS [72] Inventor:

Giorgio Bonzano, Caluso, Italy Honeywell Information Systems ItaliaS.p.A., Turin, Italy Filed: July 14, 1970 Appl. No.: 54,815

Foreign Application Priority Data I July 17, 1969 Italy ..19733 A/69Assignee:

US. Cl ..3l8/318, 197/133, 226/43, 330/30 Int. Cl. ..G05b 5/00, H02p5/00, B41j 15/00 Field ofSearch ..318/314, 318, 329, 326, 604, 318/605;197/133; 226/2, 43, 45 References Cited UNITED STATES PATENTS 2,927,2583/1960 Lippel 3....318/604 x LOGIC DEVICE 5 l REFERENCE VOLTAGE l/GENERATOR VOLTAGE 17 C OMPARATOR H AMPLIFIER [15] 3,656,041 [451 Apr.11, 1972 3,452,258 6/1969 Thompson ..318/604 3,504,362 3/ 1970 Feldmann..3 18/604 X 3,452,853 7/1969 Mabon ..226/43 X 3,323,700 6/1967 Epsteinet al. ..226/45 X Primary Examiner-J. D.v Miller AssistantExaminer-Robert J. Hickey Attorney-George V. Eltgroth, Lewis P.Elbinger, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman [57]ABSTRACT Apparatus for controlling the paper feeding in printingapparatus, wherein the feed motor speed is controlled by the combinedeffect of a speed-space detector whose output is speed-proportionalvoltage and said pulses are compared with a predetermined pulse number,and wherein the results of said comparison are employed in combinationto provide a suitable paper feed power control through a bidirectionalamplifier which does not require a stabilized power supply.

4 Claims, 6 Drawing Figures maooqqo Patented April 11, 1972 3,656,041

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AM PL|F|ER 1 r s Giorgi o BONZA N0 INVEN'I'OR.

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I ployed in information BACKGROUND OF INVENTION This invention relatesto apparatus for controlling the paper feeding in high-speed printers,particularly in printers emprocessing systems. Accordingly, thisinvention concerns apparatus for controlling the acceleration, thebraking, and the reversal of a low inertia motor according toa'predetermined sequence.

The feeding of paper in high-speed printers is usually provided by meansof a motor which drives a system of sprocket,

or toothed, wheels or chains, whose teeth engage in a set of sprocketholes provided in the paper. The distance of the paper advancement mustbe an integral multiple of a definite quantity, usually the minimumspacing between consecutive printed lines. This quantity is called theline pitch.

According to requirements, the paper may be controlled to advance, inresponse to an appropriate line feed signal, one,

, two, or even three line pitches at a time during normal printingoperations, to obtain printed texts of different densities. The papermay also be controlled to advance through a large number of line pitchesby the slew operation, in which a substantially large portion of blankspace is interposed v between portions of printed text.

Apparatus is known for precisely controlling the position of the paperat the end of each line feed or slew operation. This usually comprisesmechanical means, such pin-and-ratchet devices, gears, and the like.However, devices are costly and are subject to considerable wear andtear as a consequence of the mechanical stresses to which they aresubjected. Moreover, they are usually noisy and frequently go out ofadjustment.

Other feed control apparatus uses low inertia motors for directlycontrolling the paper feed operation. Such motors may be, for example,direct current motors with printed-circuit rotors, controlled bybidirectional amplifiers suitable for v imparting to the motor highaccelerating or decelerating torques. The paper feed operation requires,in this instance,

three states: a first state of fast acceleration, a second state of Iconstant speed and a third state of fast deceleration (braking). In thefirst state the controlling amplifier delivers a large current ofpredetermined polarity, in the second state the current delivered isonly that required to compensate for the energy lost by friction inorder to maintain the motor at constant speed, and in the third statethe amplifier delivers a large current of reversed polarity. To obtainthe same distance of line pitch in each state, the motor speed and,therefore, the amplifier current delivered in each state, must beprecisely controlled, so that, under like control conditions, the paperadvances the same number of line pitches during equal intervals.

It is therefore necessary for the motor control amplifier to have anoutput almost perfectly stable and independent of external conditions.In particular, in the prior art, great im portance is given tostabilizing the direct current source delivering the current controlledby the motor control amplifier. However, precise stabilization of alarge d-c current source is very burdensome and costly.

Therefore, it is the object of the instant invention to provide a paperfeed control system of low cost, great accuracy and high reliability.

SUMMARY OF THE INVENTION According to the invention this object isattained by supplying the motor from a bidirectional amplifier which iscontrolled by a signal provided from comparing a reference voltage and avoltage generated by a tachometric generator driven by the motor.Stabilization of the current delivered by the amplifier is obtained in asimple and efficient manner by stabilizing an intermediate stage of theamplifier utilizing low power Zener diodes.

Although the invention is primarily directed toward paper feeding in ahigh-speed printer, it may be used in a number of 2 other instanceswherein it is necessary to control acceleration, constant speed, anddeceleration and reversal a rotating mechanical device driven by alow-inertia motor. For example, the invention is useful with the tapetransport capstan of a tape handler of the single capstan type.

BRIEF DESCRIPTION OF THE DRAWING The invention will be described withreference to the accompanying drawings, wherein:

FIG. 1 is a block diagram, including a perspective view of a portion ofa high-speed printer of the invention;

FIG. 2 illustrates waveforms of various voltages and currents in theembodiment of FIG. 1;

FIG. 3 is a schematic diagram of the reference voltage generator andvoltage comparator of the invention;

FIG. 3a is a diagram of the equivalent circuit of the voltage comparatorof FIG. 3;

FIG. 4 is a schematic diagram of the bidirectional amplifier of F IG. 1;and

FIG. 5 is a schematic diagram of a variation of the amplifier of FIG. 4;

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a paperfeed motor 1 drives a toothed chain member 2. Member 2 engages sprocketholes in and thereby moves a paper web 3. Either shaft of motor 1, or onanother shaft directly driven by the motor, are mounted a photodisc 4,and a tachometric d-c generator 7. Disc 4 is provided at its peripherywith a set of uniformly spaced holes associated with a photoelectricpick-up device which comprises a lamp 5 and a photocell, or photodiode,6. Generator 7 delivers at its terminals a voltage proportional to therotational speed of motor 1.

The distance between adjacent holes on the periphery of photodisc 4corresponds to the angle through which motor 1 must rotate to advancepaper web 3 by a single line pitch. receives a light pulse, and deliversan electric pulse, each time that the paper web advances a line pitch.

The paper feeding occurs either step-by-step," each step spanning one,two or three line pitches, or by slewing," wherein the paper webadvances through a substantially larger number of line pitches. Althoughslewing may occur at different speeds, depending on amount of spacingrequired, the slew speed is always greater than the step-by-step speed.For example, three speeds may be employed: a low speed for thestep-by-step advancement, an intermediate speed for slow slewing, and ahigh speed one for fast" slewing. Possible values for these three speedsmay be 600 mm/sec., 1,000 mm/sec., and 1,800 mm/sec.

In FIG. 1, a logical device 8 receives, instruction signals on an inputlead 9. The instruction signals correspond to the required type offeeding; i.e., step-by-step feeding by one, two or three line pitches,slow slew or fast slew, and number of pitches per slew operation. Thepulses delivered by photocell 6 are supplied to logical device 8 on aninput lead 10.

Logical device 8 responds to the instruction signals to control areference voltage generator 11, which generates a reference voltage Vfor determining the rotational speed of motor 1. The reference voltagegenerated by generator 11 is applied to an input lead 12 of a comparator13. Comparator 13 compares two voltages, reference voltage V and avoltage V termed the tachometric voltage. The tachometric voltage Vwhich is proportional to the voltage generated by tachometric generator7, is applied to input lead 14. The ratio between the tachometricvoltage V and the voltage delivered by generator 7 is so chosen, thatfor each different reference voltage, the tachometric voltage providedat the corresponding motor speed is slightly lower than voltage VAssume, first, that this ratio is equal to unity, wherein voltage V isthe same as the actual voltage delivered by generator 7. In comparator13, the tachometric voltage is subtracted from the reference voltage.The difference voltage delivered by comparator 13 is aicontrol voltage Vwhich is applied to an input lead 15 of a bidirectional amplifier 16.This difference voltage may be positive, if the reference voltage ishigher than the tachometric voltage, in which case the output lead 17 ofamplifier l6 delivers a positive control current which causes motor 1 torotate in a direction appropriate for feeding the paper. If thedifference voltage is negative, amplifier 16 supplied to the motor anegative control current, which has a braking effect. If the differenceis zero, the motor is not supplied with control current.

The waveforms of FIG. 2 illustrate the reciprocal relationship betweenthe tachometric voltage V and the control volt-,

age V and illustrate the current delivered to the motor, for the exampleof a fast slewing. In this example, responding to the receivedinstruction signals, logical device 8 selects a reference voltagerepresenting the fast slew. Line R (waveform a) represents thisreference voltage V and line T represents the corresponding tachometricvoltage V Initially, when motor 1 is at rest, the tachometric voltage iszero, so that the control voltage V which is the difference betweenvoltages V and V and is represented by line S (waveform b), is equal toreference voltage V Accordingly, amplifier 16 delivers a positivecontrol current I as shown by line I (waveformr') 7 mg, I a, W 4 mm Asthe motor starts turning and increases its speed, the tachometricgenerator delivers an increasing voltage as represented by line T. Thecontrol voltage V correspondingly decreases, as shown by line S, whichis the difference between the ordinates of lines R and T. When voltage Vbecomes less than a predetermined threshold value W, corresponding tothe saturation conditions of amplifier 16, the control current out-- putI decreases from its initial maximum value I and, therefore, theacceleration and the slope of curve T decrease. When the control currentis only sufficient to compensate for frictional losses, the accelerationbecomes zero and the motor runs at constant speed.

During the rotation of motor 1, the pick-up device associated withphotodisc 4 transmits a number of pulses, equal to the number of linepitches advanced, to logical device 8. Logical device 8 counts thesepulses by means of a counter. When the number of pulses received bydevice 8 reaches a quantity n-k, wherein n is the programmed number ofline pitches of the current slew, and k is an integer suitably chosen,for example 5, reference voltage V is reduced to the value Vcorresponding to step-by-step feeding. Accordingly, V becomes lower thanV and a negative control voltage V is delivered to amplifier 16, whichthereupon delivers a negative control current I,,, This negative controlcurrent abruptly slows motor 1 and reduces its speed to the step-by-stepvalue.

This braking action requires the duration of k photodisc pulses. Whenthe n pulse is received by logical device 8 the reference voltage isreduced to zero, the control voltage V again goes negative, and thebraking current brings the motor to a halt.

It is apparent that the precision of the final position reached by thepaper web at the end of a feeding operation is conditioned by theprecision of action controlled by the braking current. If such action istoo strong, the paper web halts too early, whereas if it is too weak,the paper overshoots the intended final position.

Reference voltage generator 11, FIG. 3, comprises three transistors T Tand T for example of the NPN type. The collectors of these transistorsare supplied from a common positive voltage source, +V, (for example,+20 v) through respective resistors R R R The emitters of transistors TT and T are grounded. The collectors of transistors T T .and T are alsoconnected to the anodes of the respective diodes D,,'D and D Thecathodes of these three diodes are all connected to one end 25 of apotentiometer R whose other end is grounded. The bases of transistorsT,, T and T are connected to the respective input terminals 21, 22, 23.

device 8, which correspond to the required reference voltage to bedelivered. The control signals on terminals 21, 22, and 23 representbinary values, the binary 1 being represented by a positive voltage (forexample instance +5 V), and the'binary 0 being represented by 0 v.

When a binary 1 signal; i.e., a positive voltage, is applied to all ofthe three input terminals 21, 22, 23, the three transistors T,, T and Tconduct, their collector voltages drop practically to 0 v and,consequently, point 25 drops to 0 v. Accordingly, reference voltage V onlead 12 is at 0 v. In this instance, motor 1 is supplied with no currentand no paper feeding occurs.

If a binary 0 signal is applied to input terminal 21, while inputterminals 22 and 23 receive binary l signals, transistor T becomesnon-conductive. Current flows through resistor R,, diode D andpotentiometer R Accordingly, lead 12 is brought to a reference voltage Vwhich depends on the values of resistor R and potentiometer R and theposition of the movable tap of potentiometer R Since the resistance ofresistor R is considerably greater than that of potentiometer R thereference voltage V is substantially less than the source voltage, +V,.By adjusting the movable tap of potentiometer R the value of voltage Vis brought to that required for stepby-step feeding.

If a binary 0 signal is applied to both input terminals 21 and 22,transistors T and T become non-conductive. Resistors R and R effectivelybecome parallel connected through respective diodes D and D Theresulting resistance value is lower than in the immediately precedingcase, so that the reference voltage at lead 12 is higher, being areference voltage V required for the slow slew.

If a binary 0 is applied to both input terminals 21 and 23, resistors Rand R become effectively parallel connected. Since the value of resistorR is relatively small with respect to that of resistor R the resultingresistance value is further reduced. Therefore the voltage at lead 12 isrelatively high, being the reference voltage V required for the fastslew.

The following table gives the binary values applied to the inputterminals for each of the four control conditions, and the relatedreference voltages provided:

Condition Input Terminals Ref. Voltage No feeding l l l O Step-by-step 0l l V Slow slew 0 0 l V,

Fast slew 0 l 0 V,-

Only four of the eight possible combinations of binary values at thethree input terminals are used herein. Therefore, four remainingcombinations are available if additional reference voltages are needed.The choice of the four combinations is only representative; differentcombinations may be selected depending on the resistance values anddisposition employed. Moreover, since only four reference voltages areemployed in the preferred embodiment, only two input terminals arerequired to provide the four different combinations of applied binaryvalues. However, such an arrangement might set too rigid a constraint onthe voltage values obtainable from particular resistance values.Instead, with the disclosed arrangement the values of the threeresistances may be freely chosen to obtain the most suitable ratiobetween the three required feeding speeds.

The movable tap of potentiometer R permits adjusting the step-by-stepfeeding speed to the required value. If R represents the portion ofpotentiometer R between the movable tap and ground, the referencevoltage V is proportional to R. However, the ratios between the variousreference voltages are independent of R, depending only on R,, R R and RThus, adjusting the potentiometer tap does not change the ratios betweenthe speeds.

A set of suitable values for these resistances is, for example, thefollowing:

responding speeds are:

R R 2.2 Kohm R 400 ohm R,,= 500 ohm which provide the following set ofreference voltages:

where V is the value of the voltage source.

Thus, the ratios between reference voltages and cor- If the step-by-stepfeeding speed is, for example, 22 inches per second (560 mm/s) the slowslew speed is appr. 37 /?inches per second (950 mm/s) and the fast slewspeed is 71 inches per second (1,800 m'm/s).

Comparator 13, FIG. 3 comprises resistors R R and R connected as shown.The comparator receives the reference voltage V on lead 12 and deliversthe control voltage V on lead 15, which is the input to amplifier 16,represented in FIG.

3 by its input resistance R The tachometric generator 7 is connectedacross leads 14 and 15 and delivers a voltage V' proportional to therotational speed of motor 1, and, accordingly, to the feed rate of thepaper web. Resistors R and R form a voltage divider so that between lead15 and point 18 there is a tachometric voltage V, equal to: V, R, (RR,). The resistance values R and R, are chosen such that the tachometricvoltage V is comparable to the reference voltage V,,; i.e., for eachdifferent reference voltage V there is a rotational speed of thetachometric generator for which V is equal to V Applying Theveninstheorem of electric circuits to the circuit comprising the tachometricgenerator and resistors R and R there is derived an equivalent circuitcomprising an ideal voltage generator G delivering voltage V in serieswith a resistor R whose resistance is that of resistors R and R inparallel:

e 6 R1/ (R6 R7) Accordingly, the equivalent circuit of comparator 13 isshown in FIG. 3a, where in G is an ideal voltage generator providing thereference voltage V and R' is a resistance equal to the sum of theresistances of resistor R and the portion R of 1 potentiometer Rincluded in the circuit P. The control voltage V is the voltagedeveloped across resistance R The current I in the equivalent circuit ofFIG. 3a is given by: R" 1 eq 's c) I Since V =R I, the equation may bewritten as:

V V =[(R +R' +R R V =KV =V' where K is a constant and V' is a fictitioussignal voltage, proportional to control voltage V,.

Thus, waveforms of FIG. 2 are valid even if, in place of the voltage V'of generator 7, the effective voltage V is considered, and if, in placeof the control voltage V the fictitious signal voltage V' is taken intoaccount, because the voltage V is proportional to voltage V and voltageV' is proportional to voltage V This requires only changing the scale ofwaveforms a and 12. Moreover, for V =V V 5 =0, and

The bidirectional amplifier 16 of FIG. 4 provides the control current tomotor 1. Amplifier 16 comprises a voltage preamplifier including twodifferential amplifiers and a final stage, which include transistors T TT T and T and a current amplifier including a first stage which usescomplementary transistors T and T a second stage which usesnon-complementary transistors T and T and a final stage which uses twoparallel-connected power transistors T and T for the positive output andtwo parallel-connected power transistors T and T for the negativeoutput.

The first differential amplifier comprises the NPN transistors T and TThe collectors of transistors T and T are supplied from the stabilizedvoltage source VA, through the respective resistor R and variableresistor R The emitters of transistors T and T are connected to thecollector .of a transistor T whose emitter is connected, in turn,through a resistor R to the stabilized negative voltage source VA. Thestabilized voltage sources +VA and VA are obtained respectively from twonon-stabilized supply voltages V and V, applied to the respective supplyterminals 33 and 34. These two supply voltages are substantially equalin amplitude and are symmetrically connected with respect to a referencevoltage, which usually is the ground voltage.

Stabilization of the voltages VA and VA is provided by stabilizingcircuits comprising the respective Zener diodes Z and Z and resistors Rand R arranged according to wellknown techniques.

A Zener diode Z is connected between the emitter of transistor T and oneend of resistor R thereby maintaining, in cooperation with resistor Rthe base of transistor T at a constant voltage with respect to thestabilized negative voltage VA. Thus, the current flowing throughresistor R is maintained at a constant value and, consequently, the sumof the currents flowing rhough transistors T and T is held constant.

The base of transistor T is connected through a resistor R to input lead15, on which the control voltage V is supplied. The base of transistor Tis connected to a point 35. Point 35 is the central point of a voltagedivider comprising resistors R and R one end of such voltage dividerbeing grounded and the other end being connected to a terminal 17, whichsupplies motor 1. As it will be explained hereafter, a feed-back effectis thereby obtained.

When motor 1 is at rest, and no current flows therethrough, bothterminal 17 and point 35 are at ground voltage (0 v). If input lead'15is also at 0 v., the same amount of current must flow throughtransistors T and T Therefore, if R is equal to R' the collectors oftransistors T and T are at the same voltage. This balanced condition canbe achieved by a fine adjustment of variable resistor R if it isnecessary to compensate for differences in the intrinsic resistance ofthe transistor. However, such differences usually will be very small,inasmuch as transistors T and T are matched to have equalcharacteristics, to the extent possible.

The collector voltages of transistors T and T are applied to therespective bases of PNP transistors T and T which form the seconddifferential amplifier. The emitters of transistors T and T areconnected together and to one terminal of a resistor R which is suppliedat its other terminal from the positive stabilized voltage source +VA.The collector of transistor T is grounded. The collector of transistor Tis connected, through a resistor R to the negative stabilized voltagesource VA. This second differential amplifier is symmetrically driven bythe output signals of the first differential amplifier. The employmentof transistors of opposite conductivity type for the first and seconddifferential amplifiers substantially reduces, through thiscompensation, the effect of temperature drift.

The collector of transistor T,;, is also connected to the base oftransistor T The emitter of transistor T is connected to the stabilizednegative voltage source VA. The collector of transistor T is suppliedfrom the stabilized positive voltage source +VA through a resistor R anda diode D.

The amplifier comprising transistor T is the final stage of the voltagepreamplifier and is provided with output points 36 and 37, which differin voltage by the drop through Diode D. In the quiescent condition;i.e., in the absence of an input control voltage V the voltages atpoints 36 and 37 are balanced with respect to the ground. In thisbalanced condition the voltage at point 36 is slightly positive and thevoltage at point 37 is slightly negative.

When a positive control voltage is applied to input lead 15, theconduction of transistor T increases and correspondently the currentflowing through transistor T decreases. The voltage of the collector oftransistor T and of the base of transistor T decreases, and the voltageof the collector of transistor T and of the base of transistor T1,;increases. The resistance of transistor T and, therefore, the voltagedrop between its emitter and collector increases, whereby the voltage ofthe base of transistor T decreases. Therefore, current flowing throughtransistor TH decreases. whereupon the voltages of points 36 and 37increases. Conversely, when a negative control voltage is applied toinput lead 15. the voltages of points 36 and 37 decrease. However, thedifference between the voltages of points 36 and 37, being equal to thep r s d siegtniqssnmi i w ate ably:

The above-described voltage preamplifier is followed by a currentamplifier. The first stage of this current amplifier comprises a pair ofcomplementary transistors T and T transistor T being, for example, ofthe NPN type, and transistor T being of the PNP type. The collector oftransistor T is connected to the positive stabilized voltage source +VAthrough a resistor R and its emitter is connected to a point 38. Thecollector of transistor T is connected directly to the negativestabilized voltage source VA, and its emitter is connected to point 38through a resistor R The voltages of points 36 and 37 are applied to thebases of respective transistors T and T In the absence of an inputcontrol voltage V both of transistors T and T are in a state of lowconduction; i.e., both are close to cutoff. When a positive controlvoltage is applied to input lead 15 both points 36 and 37 changepositively, as described previously herein. Because transistors T and Tare of opposite conductivity types, transistor T becomes more conductiveand transistor T becomes less conductive.

The collector of transistor T is connected to the base of transistor TThe emitter of transistor T is connected to the base of transistor TTransistors T and T are of the PNP type and, with resistors R R R and Rform an amplifier wherein each transistor is connected as an emitterfollower. Such amplifier provides a substantial amplification of theoutput current.

Transistors T and T drive respectively a pair of transistors T and T anda pair of transistors T and T Each of transistors T T T and T withrespective sets of resistors 21, R28 29; 30 31, 32; 33, 34 35; and 36,31 R forms an emitter follower circuit. The emitter follower comprisingtransistor T is in parallel with the emitter follower comprisingtransistor T both such emitter followers being supplied by the positivesupply voltage +V. The emitter follower Transistor T is in parallel withthe emitter follower comprising transistor T both such emitter followersbeing supplied by the negative supply voltage V. In absence of an inputcontrol voltage V each of transistors T T T and T is in a state of lowconduction, being close to cutoff, so that only a relatively smallcurrent flows through these transistors from terminal 33 to terminal 34,point 38 being at v.

When a positive control voltage is applied to input lead 15, the base oftransistor T becomes more positive and transistor 15 becomes moreconductive, whereas although the base of transistor T also becomes morepositive, the conduction of transistor T decreases. Consequently, point38 becomes positive and causes a positive increase of the voltage atpoint 35, the base of transistor T Thus, the difference between thecurrents through transistor T T decreases. Thus, a negative feed-backeffect is provided, with its well-known advantages of greater stabilityand less sensitivity to noise.

The increase in conduction of transistor T and the decrease inconduction of transistor T cause a respective decrease of the basevoltage of transistor T and increase of the base voltage of transistor TThus, transistor T becomes more conductive and transistor T lessconductive. Under these conditions, the decreased voltage of the emitterof transistor T causes a conduction of transistors T and T to increase,whereas the increased voltage of the emitter of transistor T causes theconduction of transistors T and T to decrease. Transistors T and Tthereby deliver a greater positive current and transistors T and T alesser negative current to terminal 17.

As a consequence, for a positive control voltage the motor connected toterminal 17 receives a positive current and is accelerated as required.In the opposite case; i.e., wherein a negative control voltage isapplied to lead 15, a negative current is supplied to the motor, withits consequent braking effect.

Since terminal 17 is directly connected to point 38, there is no need tostabilize the supply voltage in the current amplifcation stages whichfollow complementary transistors T and T In fact, the stabilization ofthe voltage at points 31 and 32, ensures that the voltage of point 38 isaffected only by the control voltage at input lead 15 and not byaccidental fluctuation of the supply voltages +V and V.

Accordingly, the possible fluctuations of the non-stabilized voltagesupplying the following stages cannot influence the voltage of point 17,which supplies motor 1. Since the current required for the stage withthe complementary transistors T and T and the preceding stages issubstantially lower than that required for the following power stages, aremarkable saving in cost and dimensions of the components of thestabilizing circuit is attained, relative to that which would berequired for stabilizing the voltages +V and V provided at terminals 33and 34.

A satisfactory result, with even a lower cost of the stabilizingcomponents, may be provided by the arrangement illustrated in FIG. 5.The circuit of FIG. 5 differs from that of FIG. 4 in that the supplyvoltage for the complementary transistors T andv T is also notstabilized, but only the supply voltage for the preceding stages. Bythis arrangement, the stabilized voltages +VA and -VA, obtained by useof resistors R and R and Zener diodes 2. and Z are present at points 40and 41, whereas at points 31 and 32 the non-stabilized voltages +V and Vare present.

The current to be stabilized is further reduced and an additional savingthus results. In this instance the voltages of points 36 and 37, andtherefore the voltages applied to the bases of transistors T and T areindependent of fluctuations of voltages +V and V. The effect of suchfluctuations on the voltage of point 38, however, although theoreticallynot zero, is effectively negligible. In fact, this effect is reduced tothe changes in voltage drop across the base-emitter junctions oftransistors T and T due to changes in the current flowing through thesejunctions as a result of such voltage fluctuations.

I claim:

1. A device for controlling paper feed in a printing apparatus,comprising a low-inertia motor, a tachometer device for delivering atachometric voltage proportional to the paper feed speed, a pulsegenerator device for delivering a pulse each time the paper is moved adistance equal to a line pitch, a logical control device having inputsto receive command signals and pulses generated by said pulse generatordevice, a selectively controlled reference voltage generator, fordelivering a reference voltage in response to a set of control signalsgenerated by said logical control device according to the commandsignals and pulses received thereby, said reference voltage generatorcomprising first, second and third transistors having the collectorthereof supplied from a common voltage source through respective first,second and third resistors, the bases of said transistors, beingconnected to respective first, second and third input terminals, theemitters of said transistors being directly connected to ground, thecollectors of said transistors being further connected to one electrodeof respective first, second and third diodes, the other electrodes ofeach of said diodes being connected to one fixed terminal of apotentiometer, the other fixed terminal of said potentiometer beingconnected to ground, and the movable tap of said potentiometer beingconnected to the output terminal of said reference voltage generator, acomparing device for comparing a voltage proportional to saidtachometric voltage and said reference voltage and for generating asignal voltage having an amplitude depending on the difference betweensaid reference voltage and said voltage proportional to the tachometricvoltage, and a bidirectional amplifier for controlling the rotationalspeed of said low-inertia motor by means of a supply current controlledin amplitude and direction by said signal voltage,

said reference voltage generator operating to deliver to said outputterminal a particular reference voltage, selected among a plurality ofpredetermined reference voltages, in response to the patterns of signalswhen appropriate patterns of signals are applied by said logical controldevice to said reference voltage input terminals.

2. The device of claim 1, wherein said comparing device comprises firstand a second series connected resistors connected between a first inputterminal and an output terminal, a third resistor connected between thepoint common to said first and second resistors and a second inputterminal, said tachometric device applying between said output terminaland said second input terminal a tachometric voltage proportional to therotational speed of said motor, said first input terminal being directlyconnected to the output terminal of said reference voltage generator.

3. Apparatus for controlling the slewing of a print-receiving member toa precise final position in a high-speed printer in response to inputcommand signals representing the number of line pitches through whichsaid member is to be slewed, comprising: an electric motor for slewingsaid print-receiving member through a printing position, means forsensing the slewing of said print-receiving member and for delivering afirst type signal representing said slew speed and a pulse each timesaid print-receiving member moves a distance of one line pitch throughsaid printing position, first control means responsive to the receipt ofsaid input command signals for generating a reference signal having afirst value representative of a predetermined slew speed, said firstcontrol means comprising first, second and third transistors having thecollector thereof supplied from a common voltage source throughrespective first, second and third resistors, the bases of saidtransistors, being connected to respective first, second and third inputterminals, the emitters of said transistors being directly connected toground, the collectors of said transistors being further connected toone electrode of respective first, second and third diodes, the otherelectrodes of each of said diodes being connected to one fixed terminalof a potentiometer, the other fixed terminal of said potentiometer beingconnected to ground, and the movable tap of said potentiometer beingconnected to the output terminal of said first control means, secondcontrol means responsive to said input command signals and to saidpulses to generate a second type signal when said print-receiving memberrequires slewing only through a predetermined number of remaining linepitches, said first control means being responsive to said second typesignal for changing said reference signal to a second valuerepresentative of a deceleration of said motor, means for delivering athird type signal representing the algebraic difference between saidreference signal and said first type signal, and means responsive tosaid third type signal to control the speed of said motor.

4. Apparatus for controlling the slewing of a print-receiving member toa precise final position in a high-speed printer in response to inputcommand signals representingthe number of line pitches through whichsaid member is to be slewed comprising: an electric motor for slewingsaid printreceiving member through a printing position, a speed-sensingmember for sensing the speed of slew of said print-receiving member andfor delivering a first type signal representing said slew speed, a linepitch sensing member for sensing the slewing of said print-receivingmember and for delivering a pulse each time said print-receiving membermoves a distance of one line pitch through said printing position, firstcontrol means responsive to receipt of said input command signals forgenerating a reference signal having a first value representative of apredetermined slew speed, said first control means comprising first,second and third transistors having the collector thereof supplied froma common voltage source through respective first, second and thirdresistors, the bases of said transistors, being connected to respectivefirst, second and third input terminals, the emitters of saidtransistors being directl connected to round, the collectors of saidtransistors being urther connec ed to one electrode of each of saiddiodes being connected to one fixed terminal of a potentiometer, theother fixed terminal of said potentiometer being connected to ground,and the movable tap of said potentiometer being connected to the outputterminal of said first control means, second control means responsive tosaid input command signals and to said pulses to generate a second typesignal when said print-receiving member has been slewed through thenumber of line pitches represented by said input command signals less apredetermined number of line pitches, said first control means beingresponsive to said second type signal for changing said reference signalto a second value representative of a deceleration of said motor, meansfor comparing said reference signal and said first type signal fordelivering a third type signal representing the algebraic differencebetween said reference signal and said first type signal, and meansresponsive to said third type signal to control said motor to acceleratesaid print-receiving member to said predetermined slew speed after saidapparatus receives said input command signal and, after said second typesignal has been generated, for decelerating said print-receiving memberto stop after having been slewed through the precise member of linepitches represented by said input command signals.

1. A device for controlling paper feed in a printing apparatus,comprising a low-Inertia motor, a tachometer device for delivering atachometric voltage proportional to the paper feed speed, a pulsegenerator device for delivering a pulse each time the paper is moved adistance equal to a line pitch, a logical control device having inputsto receive command signals and pulses generated by said pulse generatordevice, a selectively controlled reference voltage generator, fordelivering a reference voltage in response to a set of control signalsgenerated by said logical control device according to the commandsignals and pulses received thereby, said reference voltage generatorcomprising first, second and third transistors having the collectorthereof supplied from a common voltage source through respective first,second and third resistors, the bases of said transistors, beingconnected to respective first, second and third input terminals, theemitters of said transistors being directly connected to ground, thecollectors of said transistors being further connected to one electrodeof respective first, second and third diodes, the other electrodes ofeach of said diodes being connected to one fixed terminal of apotentiometer, the other fixed terminal of said potentiometer beingconnected to ground, and the movable tap of said potentiometer beingconnected to the output terminal of said reference voltage generator, acomparing device for comparing a voltage proportional to saidtachometric voltage and said reference voltage and for generating asignal voltage having an amplitude depending on the difference betweensaid reference voltage and said voltage proportional to the tachometricvoltage, and a bidirectional amplifier for controlling the rotationalspeed of said low-inertia motor by means of a supply current controlledin amplitude and direction by said signal voltage, said referencevoltage generator operating to deliver to said output terminal aparticular reference voltage, selected among a plurality ofpredetermined reference voltages, in response to the patterns of signalswhen appropriate patterns of signals are applied by said logical controldevice to said reference voltage input terminals.
 2. The device of claim1, wherein said comparing device comprises first and a second seriesconnected resistors connected between a first input terminal and anoutput terminal, a third resistor connected between the point common tosaid first and second resistors and a second input terminal, saidtachometric device applying between said output terminal and said secondinput terminal a tachometric voltage proportional to the rotationalspeed of said motor, said first input terminal being directly connectedto the output terminal of said reference voltage generator.
 3. Apparatusfor controlling the slewing of a print-receiving member to a precisefinal position in a high-speed printer in response to input commandsignals representing the number of line pitches through which saidmember is to be slewed, comprising: an electric motor for slewing saidprint-receiving member through a printing position, means for sensingthe slewing of said print-receiving member and for delivering a firsttype signal representing said slew speed and a pulse each time saidprint-receiving member moves a distance of one line pitch through saidprinting position, first control means responsive to the receipt of saidinput command signals for generating a reference signal having a firstvalue representative of a predetermined slew speed, said first controlmeans comprising first, second and third transistors having thecollector thereof supplied from a common voltage source throughrespective first, second and third resistors, the bases of saidtransistors, being connected to respective first, second and third inputterminals, the emitters of said transistors being directly connected toground, the collectors of said transistors being further connected toone electrode of respective first, second and third diodes, the otherelectrodes of each of said diodes being connected to one fixed terminalof a potentiometer, the other fixed terminal of said potentiometer beingconnected to ground, and the movable tap of said potentiometer beingconnected to the output terminal of said first control means, secondcontrol means responsive to said input command signals and to saidpulses to generate a second type signal when said print-receiving memberrequires slewing only through a predetermined number of remaining linepitches, said first control means being responsive to said second typesignal for changing said reference signal to a second valuerepresentative of a deceleration of said motor, means for delivering athird type signal representing the algebraic difference between saidreference signal and said first type signal, and means responsive tosaid third type signal to control the speed of said motor.
 4. Apparatusfor controlling the slewing of a print-receiving member to a precisefinal position in a high-speed printer in response to input commandsignals representing the number of line pitches through which saidmember is to be slewed comprising: an electric motor for slewing saidprint-receiving member through a printing position, a speed-sensingmember for sensing the speed of slew of said print-receiving member andfor delivering a first type signal representing said slew speed, a linepitch sensing member for sensing the slewing of said print-receivingmember and for delivering a pulse each time said print-receiving membermoves a distance of one line pitch through said printing position, firstcontrol means responsive to receipt of said input command signals forgenerating a reference signal having a first value representative of apredetermined slew speed, said first control means comprising first,second and third transistors having the collector thereof supplied froma common voltage source through respective first, second and thirdresistors, the bases of said transistors, being connected to respectivefirst, second and third input terminals, the emitters of saidtransistors being directly connected to ground, the collectors of saidtransistors being further connected to one electrode of each of saiddiodes being connected to one fixed terminal of a potentiometer, theother fixed terminal of said potentiometer being connected to ground,and the movable tap of said potentiometer being connected to the outputterminal of said first control means, second control means responsive tosaid input command signals and to said pulses to generate a second typesignal when said print-receiving member has been slewed through thenumber of line pitches represented by said input command signals less apredetermined number of line pitches, said first control means beingresponsive to said second type signal for changing said reference signalto a second value representative of a deceleration of said motor, meansfor comparing said reference signal and said first type signal fordelivering a third type signal representing the algebraic differencebetween said reference signal and said first type signal, and meansresponsive to said third type signal to control said motor to acceleratesaid print-receiving member to said predetermined slew speed after saidapparatus receives said input command signal and, after said second typesignal has been generated, for decelerating said print-receiving memberto stop after having been slewed through the precise member of linepitches represented by said input command signals.